The present invention relates to a flat stacked-type conductive polymer actuator that can expand a displacement by using stacked layers.
Due to the social background with the declining birthrate and the growing proportion of elderly people, there have been increasing needs to a machine working in the neighborhood of a person or in cooperation with a person, such as home-use robots. In this case, from the viewpoints of flexible movements to deal with complicated tasks and safety in case of crash with a person, there have been increasing expectations for an artificial muscle actuator which has a flexible characteristic like the muscle of the human being. For the artificial muscle actuator such as those using pneumatic pressure, various materials or control systems have been proposed. As one of these, in recent years, an actuator that uses a conductive polymer has been devised.
As one example of conventional actuators using conductive polymers, an actuator that utilizes a transformation of the bimorph type has been proposed (for example, see Patent Document 1: Japanese Unexamined Patent Publication No. 11-169393).
FIGS. 10A, 10B, and 10C show a conventional conductive polymer actuator described in Patent Document 1. FIG. 10A shows a structure in which a solid electrolyte molded body 51 is sandwiched between polyaniline film members 50a and 50b serving as conductive polymer films. Upon turning a switch 52 on, an electric potential difference set in a power supply 53 is applied between the polyaniline film members 50a and 50b so that, as shown in FIG. 10B, anions 54 are inserted into the one polyaniline film member 50b to be expanded, while anions 54 are separated from the other polyaniline film member 50a to be contracted, resulting in that a transformation of the bimorph type is generated. In a case where the electric potential difference is reversed, as shown in FIG. 10C, the transformation is generated in a direction reversed to that of FIG. 10B.
In this structure, the transformation is generated by a difference between the amounts of displacements of the two conductive polymer films 50a and 50b functioning as electrodes. In contrast, there has been known another structure in which, by preparing an electrolyte retention layer into a liquid or gel substance, the influences of the two electrodes are prevented from being exerted on each other so that only the displacement of one of the conductive polymers is taken out to carry out expansion/contraction as an actuator. In this case, the electrode that is not utilized for the transformation is not necessarily required to be a conductive polymer and a metal electrode is mainly used, on which a conductive polymer may be formed thereon.
Since such a conductive polymer actuator generates a stress equivalent to that of a muscle at a comparatively low voltage of 1.5 V to 3.0 V, it is expected to be put into practical use as an artificial muscle.
As the liquid or gel electrolyte retention layer, an ionic liquid, which is defined as a fused salt at room temperature, is used. The ionic liquid has drawn public attentions as a new functional liquid, and 1-butyl-3-methyl imidazolium or bis(trifluoromethylsulfonyl) imide has been known as the ionic liquid, in which charges of cations and anions are delocalized, so that only little Coulomb force is exerted between the two ions so as to be kept as a liquid at room temperature. Its vapor pressure is low to hardly cause vapor loss, and this liquid is nonflammable and usually superior in thermal and oxidization stability as well as has a high lubricating characteristic. This ionic liquid is applied to an insulating sheet or the ionic liquid itself is gelled so that the electrolyte retention layer is formed.
Moreover, since the conductive polymer is a film, a method has been proposed in which, by forming the conductive polymer film into a cylindrical shape, the conductive polymer film is prevented from being buckled so as to have rigidity (for example, see Patent Document 2: Japanese Unexamined Patent Publication No. 2006-125396). As shown in FIG. 11A, conductive polymer films 60a and 60b of two kinds for expansion and contraction are alternately disposed in a circumferential direction, and end portions of an inner cylindrical member 61a and an outer cylindrical member 61b are coupled to the films in a manner so as to be crossed with each other. Therefore, when one of the two kinds of conductive polymer films 60a and 60b is expanded, the other conductive polymer film holds a load so as to exert rigidity. FIG. 11B shows one example of a layout of the conductive polymer films 60a and 60b in the circumferential direction. Moreover, as shown in FIG. 11C, a method is also proposed in which, by preparing these cylindrical members as conductive polymer members 62a and 62b, the amounts of displacements are increased.
Moreover, as shown in FIG. 12, an actuator is proposed which exerts a driving force in an expanding direction and rigidity in a contracting direction without the necessity of applying a pre-load, in a structure in which conductive polymer films 70a and 70b are stacked in a crossed pattern, by connecting with use of a link mechanism 71 that mutually converts one displacement in the expanding direction to another displacement in the contracting direction (for example, see Patent Document 3: Japanese Patent No. 3817259).
Moreover, as shown in FIGS. 13A and 13B, a piezoelectric actuator is disclosed which can expand the amounts of displacements by both of expansion and contraction, with rigidity being maintained in the expanding and contraction directions (for example, see Patent Document 4: Japanese Unexamined Patent Publication No. 63-289975).
However, the actuators having the above-mentioned structures also have issues.
In the method of Patent Document 1, since the deformation of the bimorph type is utilized, it is difficult to freely change the displacement expanding or a stress expanding by further stacking the conductive polymer films. Although the length of the conductive polymer film can be changed so as to expand the displacement and the width of the conductive polymer film can be expanded so as to expand the stress, it is not possible to stack a plurality of conductive polymer films. This structure has difficulties in stacking the layers because electric short circuiting occurs due to the fact that the polarities of the adjacent conductive polymer films are reverse to each other and reductions in stress and displacement occur due to frictional resistance caused by the fact that the adjacent conductive polymer films are reversed to each other in expansion/contraction.
In the method of Patent Document 2, by forming the conductive polymer film into a cylindrical shape so as to provide rigidity, and by providing the structure in which, as shown in FIG. 11A, two kinds of films 60a and 60b that expand and contract in a circumferential direction of cylindrical members 61a and 61b are alternately aligned in the width direction, an issue arises in which effective insertion and separation of ions through the electrolyte retention layer are difficult, which is greatly different from the structure of Patent Document 1 shown in FIG. 10A in which the surfaces of the conductive polymer films face each other in the thickness direction. Even with an arrangement, unlike the arrangement shown in FIG. 11B, with a higher density in the circumferential direction, the efficiency of the ion mobility between the adjacent conductive polymer films would be lowered in comparison with the structure in which the surfaces of the polymer films face each other. Consequently, it is difficult to output a sufficient stress and displacement as an actuator. Moreover, in the structure shown in FIG. 11C, since no specific descriptions are made to a supporting member corresponding to the cylindrical member, buckling is generated in the conductive polymer films 62a and 62b, with a result that the actuator is not functional.
In the method of Patent Document 3, as shown in FIG. 12, the driving force in the expanding direction and rigidity in the contracting direction can be achieved without applying a pre-load in both of the expansion and contraction; however, there are disadvantages that directions in which the driving force can be taken out are dispersed into two directions crossing perpendicularly with each other, and that even when the number of the conductive polymer films 70a and 70b to be stacked is increased, the displacement cannot be increased.
In the method of Patent Document 4, as shown in FIGS. 13A and 13B, the amounts of displacements can be expanded in both of the expansion and contraction with rigidity in the expanding direction as well as in the contracting direction being maintained. However, this structure uses a solid member referred to as a piezoelectric body. If the structure uses a conductive polymer film, an issue of buckling is caused as shown in FIG. 13C. Since the conductive polymer film is not a solid material but is a film, a tension is exerted when pulled from the two ends, while in contrast, buckling might be caused when compressive stresses are applied from the two sides. In other words, in the structure in FIG. 13A, rigidity can be maintained in none of the expanding direction and the contracting direction.
In order to solve the conventional issues described above, an object of the present invention is to provide a flat stacked-type conductive polymer actuator that has rigidity and a driving force in both of the contracting direction and expanding direction, as well as can expand displacement by staking layers.